1. Field of the Invention
The present invention concerns treating the surface of various polymers such that they are useful for static charge dissipation, electromagnetic induction shielding, or electroplating, and the like. Typically, these methods of treatment include depositing copper sulfide on the surface of the polymer so that the surface of the polymer becomes conductive. In particular, the present invention is a novel method for treating the surface layer of the polymers with cuprous ion to produce therein a copper sulfide composite so that the surface will be conductive. Additionally, the present invention relates to a composite material comprising a polymer whose surface has been treated so that dendritic crystals of copper sulfide are integrally incorporated within the polymer.
2. Prior Art
Different methods of applying copper sulfide to the surface of various polymers are known in the prior art. These prior art processes include many steps to incorporate the copper sulfide into the polymer surface. The prior art patents generally treat the polymer chemically in order to form copper sulfide. The chemical treatment can consist of swelling the polymer, blending within the voids of the polymer elemental sulfur, reversing the swelling such that the polymer shrinks to approximately its original dimensions, and reacting the polymer/sulfur blend with a copper compound to form a copper sulfide layer on the polymer. The following U.S. patents are exemplary of such prior art processes.
U.S. Pat. No. 3,682,786 to Brown et al. discloses plastic substrates, such as polypropylene or ABS, for example, which are treated with a solution or dispersion of sulfur in a suitable swelling solvent, such as trichloroethylene; contacted with an aqueous solution of a cuprous salt, such as cuprous chloride; and electroplated to form a coating of the desired metal. During the treatment of the plastic substrate with the sulfur-containing solvent solution, the surface of the plastic substrate swells and the sulfur-containing solvent solution is carried into the surface. Sulfur is trapped in the surfaces of the plastic substrate once the plastic substrate shrinks when removed from the chlorinated solvent (trichloroethylene).
U.S. Pat. No. 4,604,427 to Roberts et al. discloses a chemical method of forming an electrically-conductive polymer blend which comprises impregnating a non-porous, swellable or soluble host polymer with one or more cyclic compounds consisting of pyrrole aniline and substituted analogs thereof, and at least one chemical oxidant selected from the group consisting of trivalent and tetravalent compounds, such as copper, silver, cerium, molybdenum, chromium and tungsten, said oxidant being dissolved in a solvent capable of swelling or solubilizing said host polymer.
The prior art processes incorporate many steps, produce only limited results, and are expensive by comparison with the present invention.
Due to the limitations on the prior art processes and the products produced, there is a need for an inexpensive process to treat polymer surfaces. Additionally, there is a need to treat the entire thickness of a polymer film, for example, such that the polymer may be more useful than merely for electroplating. For example, the treated polymers could be useful as semiconductors which would require a current to be transmitted through a film of the treated polymer. Prior art processes, which are only treated on their surfaces, cannot be employed in such applications.
Lastly, the use of organic solvents to swell the polymer is not desirable due to health and safety reasons, and because the polymer must be carefully dried to remove residual solvent. The removal of solvent would be especially important if the surface were to be electroplated.
It is a chief aim of the present invention to develop a simpler method to make polymers conductive. It is also an aspect of the present invention to form a treated polymer different from prior art polymers in that it is capable of being conductive throughout its entire thickness.
It is also a feature of the present invention to make a polymer conductive without using organic swelling agents and thus avoid health and safety considerations of the prior art.